Re: [PATCH] ppc highmem fix

[Paolo Galtieri]

On Mon, 2005-10-10 at 16:20 -0700, Paolo Galtieri wrote:
> I've noticed that the calculations for seg_size and nr_segs in
> __dma_sync_page_highmem() (arch/ppc/kernel/dma-mapping.c) are wrong.
> The incorrect calculations can result in either an oops or a panic when
> running fsck depending on the size of the partition.  The problem with
> the
> seg_size calculation is that it can result in a negative number if size
> is offset > size.  The problem with the nr_segs caculation is returns
> the
> wrong number of segments, e.g. it returns 1 when size is 200 and offset
> is 4095, when it should return 2 or more.
> 
> Here is the patch to fix the problem.
> 
> --- linux-2.6.14-rc3-git8/arch/ppc/kernel/dma-mapping.c 2005-10-10
> 13:55:37.000000000 -0700
> +++ linux-2.6.14/arch/ppc/kernel/dma-mapping.c  2005-10-10
> 13:57:51.000000000 -0700
> @@ -401,10 +401,10 @@
>  static inline void __dma_sync_page_highmem(struct page *page,
>                 unsigned long offset, size_t size, int direction)
>  {
> -       size_t seg_size = min((size_t)PAGE_SIZE, size) - offset;
> +       size_t seg_size = min((size_t)(PAGE_SIZE - offset), size);
>         size_t cur_size = seg_size;
>         unsigned long flags, start, seg_offset = offset;
> -       int nr_segs = PAGE_ALIGN(size + (PAGE_SIZE - offset))/PAGE_SIZE;
> +       int nr_segs = 1 + ((size - seg_size) + PAGE_SIZE - 1)/PAGE_SIZE;
>         int seg_nr = 0;
> 
>         local_irq_save(flags);
> 
> 
> Paolo Galtieri (pgaltieri@xxxxxxxxxx)
> 

I want to apologize in advance for the previous post.  When I included
the patch inline I dropped the tabs :-(.  Here is the correct patch with
tabs:

--- linux-2.6.14-rc3-git8/arch/ppc/kernel/dma-mapping.c	2005-10-10
13:55:37.000000000 -0700
+++ linux-2.6.14/arch/ppc/kernel/dma-mapping.c	2005-10-10
13:57:51.000000000 -0700
@@ -401,10 +401,10 @@
 static inline void __dma_sync_page_highmem(struct page *page,
 		unsigned long offset, size_t size, int direction)
 {
-	size_t seg_size = min((size_t)PAGE_SIZE, size) - offset;
+	size_t seg_size = min((size_t)(PAGE_SIZE - offset), size);
 	size_t cur_size = seg_size;
 	unsigned long flags, start, seg_offset = offset;
-	int nr_segs = PAGE_ALIGN(size + (PAGE_SIZE - offset))/PAGE_SIZE;
+	int nr_segs = 1 + ((size - seg_size) + PAGE_SIZE - 1)/PAGE_SIZE;
 	int seg_nr = 0;
 
 	local_irq_save(flags);

Paolo

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